Photoelectric apparatus for document counting and overlap detection

ABSTRACT

Electronic counting and control means are provided which are sensitive to the transmissivity of light and include feedback means for controlling the brightness of the light source to extend its life. Additionally, integrating means are provided for determining when there is an overlap of documents being handled by the counting means. Further, specific circuit arrangements are provided for insuring that an exact count is obtained even when perforated documents are being counted and there is a gap between successive documents.

BACKGROUND OF THE INVENTION

In document handling devices of the type described for example in U.S.Pat. No. 4,054,092 issued Oct. 18, 1977 and assigned to the assignee ofthe present invention, there is taught therein apparatus for bottomfeeding of documents placed in an infeed hopper, and passage through aregion containing feed means and stripper means to separate documents soas to be passed from the aforesaid region toward an outfeed stacker on aone at a time basis, the stripping action serving to assure the deliveryof single fed documents under normal conditions.

As the documents leave the aforesaid region, they come under theinfluence of acceleration means which abruptly accelerates the documentwhich has just left the influence of the drive and stripper means so asto form a gap of at least a predetermined length between the documentbeing accelerated and the next succeeding document to be accelerated.This gap is utilized, in conjunction with light means such as an LED andlight sensing means such as a phototransistor to detect the change inbrightness in order to distinguish the movement of a document betweenthe light source and light sensing element from the passing of a gaptherebetween.

The documents continue to move from this location where they are neatlystacked in an outfeed stacker.

In many operations it is quite often necessary to be absolutely assuredthat the document count be exact. For example, when counting currencyand especially when counting currency of large denominations, an errorin the count of documents, no matter how small, is nevertheless causefor great concern.

One of the problems which contributes to the possibility that sucherrors might occur is the possibility that the currency, when in use,may acquire or have deposited thereon sticky or adhesive material or mayhave creases or other mutiliations which cause two documents to adhereto one another and to fail to separate even as a result of the strippingoperation. If two such documents are fed so that one is directlysuper-imposed upon the other, the apparatus will count this anomaly as asingle document, thus throwing off the count. It is therefore imperativein many applications to provide means for positively and reliablydetecting such conditions.

In addition to the above, and due to the fact that the documents beingcounted may be vastly different in age and amount of use, as well as thefact that they may be fed in any one of four different orientations, theproblem of distinguishing between single fed documents and double feddocuments is compounded.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is characterized by utilizing a comparator andintegrator technique for accurately and reliably distinguishing betweensingle and double fed documents.

The light source and photo-transistor cooperate with one another as wasmentioned hereinabove so that the photo-transistor output is availableas the signal to be analyzed for purposes of distinguishing betweensingle and double fed documents.

In addition to the above, novel current amplification means is utilizedwithin a feedback circuit coupled between the photo-transistor and lightsource to adjust the brightness output of the light source as a functionof the activity of the photo-transistor.

Adjustable current limiting means are also employed in conjunction withthe LED so as to cause the LED to generate light within a brightnessrange which limits the operating range of the photo-transistor to thatportion of its output current versus input characteristic curve so thatthe photo-transistor operates over that portion of the curve in whichthe greatest difference is developed in output current when the lightdirected toward the photo-transistor is attenuated by single and doublefed documents.

Comparator means compares the output signal of the photo-transistorfeedback circuit against a predetermined threshold. Since the lighttransmission characteristics of single fed documents may be the same fordouble fed documents over at least portions of their surfaces, thecomparator output signal is filtered or integrated to distinguish doublefed from single fed documents by the number of transitions or, anotherway of characterizing the situation is by the total integrated value ofthe transitions over the length of the document measured in the feeddirection.

Means are provided for setting the threshold level dependent upon thetype and nature of the documents being handled and/or counted. A"warning" circuit is provided to protect the user against thepossibility of either switching to the incorrect setting or failing toswitch from the previous setting for another type of document when a runof different type of documents is to be initiated. In this circuit,means are provided for generating a "doubles" indication when thesetting provides too much brightness. The normal doubles detectioncircuit will provide a doubles indication even for single fed documents,when the selected setting provides insufficient brightness.

The control system is provided with further means for detecting thepresence of even slightly overlapping documents through the employmentof a time-out circuit which may be comprised of either integration meansand comparator means or a counter circuit which may utilize a countpulse signal level for enabling pulses from a constant output frequencyoscillator to be accumulated in the counter, whereby the time betweenpulses represents distance travelled or alternatively by accumulatingpulses from a speed sensing means comprised, for example, of a magnetictiming gear rotated in synchronism with the rollers driving thedocuments and magnetic sensor means for generating pulses representativeof the timing gear teeth passing the sensor means.

A novel means is provided for counting the documents and for preventingholes, punches, tears or other mutilations within a document from beingfalsely interpreted as a gap between documents so as to assure a propercount. This is accomplished by counting pulses through either of the twoabove techniques mentioned in connection with the counter time-outcircuit for accumulating the train of pulses in a first counter duringperiods in which the counter photo-transistor detects light from thecounter LED of a high intensity or brightness and for accumulating saidtrain of pulses in a second counter during those intervals in which thephoto-transistor detects a reduced brightness output from the countingLED. A count of sufficient length indicates the presence of a gapbetween adjacent fed documents to develop a count pulse while a countexceeding a predetermined quantity in the first of said countersprovides a time-out signal indicative of the fact that overlappingdocuments have passed through the device. This technique greatlyimproves the counting accuracy and the ability to discriminate betweennormal gaps between documents and punched holes, mutilations and thelike within documents.

OBJECTS OF THE INVENTION AND BRIEF DESCRIPTION OF THE FIGURES

It is therefore one object of the present invention to provide a novellight source and light detector circuit incorporating brightness controlmeans for increasing circuit sensitivity and significantly increasingcomponent life.

Another object of the present invention is to provide a novel detectioncircuit for detecting the presence of double fed documents and employingintegrating means and comparator means to successfully distinguishbetween single and double fed documents.

Another object of the present invention is to provide novel documentcounting means comprising first and second counting means cooperatingwith light source and photo-detector means for counting pulses in thefirst counter as documents pass between the light source and detectormeans and for accumulating pulses in the second counter as the gapbetween documents passes between the light source and detector meanswhereby the accumulation of at least a predetermined count in one ofsaid counters is utilized to provide an accurate count of the documentsbeing handled by the document handling device.

Still another object of the present invention is to provide a documentcounting device of the type described here and above and employing speedsensor means.

The above as well as other objects of the present invention becomeapparent when reading the accompanying description and drawings inwhich:

FIGS. 1a through 1e show plots useful in describing the novel circuitryof the present invention.

FIG. 2 is a schematic diagram of a doubles detection circuit designed inaccordance with the principles of the present invention.

FIG. 3 is a schematic diagram of a time-out circuit designed inaccordance with the principles of the present invention for identifyingoverlapping documents in the document handling device.

FIGS. 3a and 3b are schematic diagrams showing document overlap.

FIG. 4 is a schematic diagram showing a counting circuit utilized inconnection with document handling devices and incorporating theprinciples of the present invention.

FIG. 5 shows a magnetic sensing circuit which may be utilized with thecounting circuit of FIG. 4, and FIG. 6 shows circuitry for selecting oneof the circuits of FIGS. 4 and 5 to drive the counters.

FIG. 7 is a more detailed schematic of the counting apparatus of FIG. 4.

FIG. 8 is a schematic diagram of a doubles detection circuit adapted toidentify a double feed condition and/or halt the handling operation andis also useful in providing a semi-automatic brightness setting.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

The electronic sensing and control circuitry to be described herein indetail is useful with document handling and counting devices andespecially that apparatus taught in U.S. Pat. No. Re. 29,470 reissuedNov. 8, 1977 and assigned to the assignee of the present invention.

A detailed description of the document handling and counting apparatusdescribed therein will be omitted herein for purposes of simplicity. Forpurposes of understanding the present invention it is sufficient tounderstand that such apparatus accepts documents in an infeed hopper,advances the documents to a combination of feeding and stripping rollerswhich corrugate the documents i.e. urge them into an undulatingconfiguration so as to cause the documents to be fed single file throughthe feeding and stripping rollers in order to be advanced toacceleration rollers for abruptly accelerating the feeding velocity ofthe documents to provide gaps of a predetermined dimension betweenadjacent edges thereof, the distance of length of said gaps beingmeasured in the feed direction. A suitable light source such as a LEDand a light sensitive means such as a photo-transistor, are positionedon opposite sides of the path of movement of the documents after theaforementioned gaps are formed for the purpose of counting thedocuments.

Apparatus of the type described here and above is capable of handlingand counting documents at speeds of the order of over 600 to 1200documents per minute thus yielding a device which is extremelyadvantageous for use in counting and/or endorsing items such as checks,food stamps, paper currency, coupons and the like.

Since documents of the above mentioned categories may have rathersignificant value such as, for example, paper currency, in applicationswherein it is desired to form batches of the paper currency of apredetermined quantity, it is extremely important to be able to form andcount such batches with the highest precision which is practical ofbeing obtained. In many situations the capability of forming batches ofprecise quantities may not be the fault of the equipment. For example,two bills may stick together as a result of having been folded orcreased or having come into contact with a glue, adhesive or othersticky substance which makes it a practical impossibility to separatethe paper currency even when using the most advanced equipmentavailable. It thus becomes extremely advantageous to provide apparatusfor detecting the presence of double fed documents in order to abruptlyhalt the equipment and thereby identify the double fed condition,typically by causing the double fed documents to be the last ones fedinto the outfeed hopper.

The technique utilized for doubles detection is to provide a lightsource such as the LED shown in FIG. 1a and a photo-transistor Ptrespectively arranged on opposite sides of the path of movement ofdocuments as represented by arrow A. The figure shows two such documentsS1 and S2 moving in the direction shown by arrow A as a result of thedocument handling apparatus referred to here and above and disclosed inU.S. Pat. No. Re. 29,470 Light from the LED is directed toward thephoto-transistor which functions in a manner such that its conductivitychanges in direct proportion to the magnitude of light striking thephoto-transistor. The plot shown in FIG. 1b shows a curve C1representing the relationship between increasing intensity of lightreaching the photo-transistor and plotted against the current generatedby the photo-transistor. Curve C1 can be seen to reach a plateau at alight intensity value v1 which basically indicates that the transistorhas saturated. Thus any increase in intensity of light above the valuev1 causes an insignificant change in the magnitude of current generatedby the photo-transistor. The vertical line through the value v0represents the intensity of light when no documents are passing betweenthe LED and the photo-transistor. It can be seen that the amount oflight intensity generated by the LED should preferably be regulated soas to cause the photo-transistor Pt to function at and below the "knee"portion of curve C1 so as to generate the most significant differencesin current magnitude responsive to the amount of light transmittedthrough single fed documents and double fed documents. Assuming properregulation, the cross-hatched area A1 which lies between the intensityvalues v2 and v3, represents the range of brightness or light intensityreaching the photo-transistor after passing through a particular type ofdocument which, for example, may be U.S. paper currency of one dollardenomination. The right hand end of this range, i.e. the value v3represents the amount of light intensity reaching the photo-transistorfor new, clean paper currency while the value v2 represents the amountof light reaching the photo-transistor during the time in which an oldone dollar bill is passing therebetween, the drop in light intensityreaching the photo-transistor being a function of the smudges or otherforeign matter which may have accumulated on the bill as a result of itslength of use and the type of handling it has undergone.

In a similar fashion, the cross-hatched area A2, defined by the verticallines v4 and v5, represents the range of light intensity reaching thephoto-transistor from the LED when two double fed bills passtherebetween. In a similar fashion, the right hand end v5 of theintensity range represents the double feeding of two crisp new billswhile the left hand end v4 of the range represents the feeding of twoold and well used bills. Other factors tending to affect light intensityare the orientation of the bills and combination of orientation of twobills when double fed.

As a practical matter, although the two areas A1 and A2 are shown asbeing separate from one another, it should be understood that it iscommon to expect that these ranges will in fact overlap, which is morethe rule than the exception, thus further complicating thediscrimination of single and double feeds.

In any case, it is most advantageous to control the light intensityreaching the photo-transistor to lie within the limits of the positiveslope at and below the "knee" of curve C1 in order to be assured thatthe largest differences in current output of the photo-transistor aredeveloped to more easily distinguish between each of the possible feedconditions. For example, if the LED were operated so that the lightintensity for the single fed and double fed bills whose ranges are givenby the cross-hatched areas A1 and A2, were to be shifted for example tothe region between the values v1 and v0, even though changes inintensity occur over this range, the current output of thephoto-transistor can be seen to change insignificantly and, as apractical matter not at all, so as to provide no practical method fordetecting the difference between single fed and double fed documents.The aforesaid adjustment is controlled by providing suitable currentcontrol or current limiting means as will be more fully described hereand below.

Turning to a consideration of FIG. 1c, the "ideal" condition is showntherein wherein the waveform W1 represents the passage of a paperdocument (such as U.S. paper currency) between the LED and thephoto-transistor Pt and amplification and inversion by amplifierwherein, at time t1 the leading edge of a square pulse is generated andthe pulse reaches a value "1" in the presence of a single bill. Thelevel remains constant at "1" over the entire length of the bill(assuming the "ideal" bill has a uniform light transmissioncharacteristic over its surface) and at time t2 the trailing edge of thesquare pulse is formed at which time the trailing edge of the documentpasses the LED and photo-transistor.

In a similar fashion, presuming two such "ideal" bills are firmly gluedtogether, the dotted curve of FIG. 1c results wherein at time t1, theleading edge of the waveform W₁ is generated and the square pulsereaches a value of "2", remains constant until time t2 at which time thetrailing edge is formed as the two double fed documents pass beyond theLED and photo-transistor. These very ideal wave shapes make it a simplematter to compare the resulting signals for single and double feddocuments in a comparator by establishing a threshold level representedby the dotted line Th1 is preferably half the distance between thevalues "1" and "2", i.e. which is one and one half (11/2) voltspresuming the other values to be one volt and two volts respectively.

Although the above solution is most satisfactory when dealing with"ideal" bills and conditions, as a practical matter this does notrepresent the true conditions obtained during document handling andcounting. The more realistic picture is represented by the waveforms W2and W3 shown in FIG. 1d wherein at time t1 waveform W2 undergoes nochange and, in fact undergoes no change until the value t1+Δt occurs atwhich time a small spike results due to an increase in the lighttransmission characteristic of the bill. The remainder of the curve canbe seen to be quite erratic.

A rather similar result can be seen to result when double fed documentspass between the photo-transistor and LED with the exception that thecurve can be seen to jump to a significantly higher value at time t1.

From a consideration of these two waveforms which more truly representactual operating conditions, it becomes much more difficult to establisha threshold level which can be relied upon to distinguish double feddocuments from single fed documents in every case. For example,considering the threshold level represented by dotted line Th2, althoughthe curve W3 can be seen to lie above this level for a greater period oftime than waveform W2, it can nevertheless be seen that the waveform W2does make transitions which surpass this level. By setting an evenhigher threshold Th3 it can be seen that the wave form W3 does not lieabove this threshold level over the entire time interval and in fact thewaveform W2 can be seen to rise above this threshold level for at leasta brief portion of the time interval t1-t2.

However, it has been observed that when the proper threshold level isselected for the type of bills being handled, single fed documents willmake only a frew transitions above the threshold level while double feddocuments will make a number of transitions above the threshold levelsaid number being significantly greater than the transitions made by thesingle fed documents. Thus it is possible through the circuitry to bedescribed to achieve a high precision doubles detection circuit throughfiltering and comparator techniques which are embodied in the doublesdetection circuitry 10 shown in FIG. 2 which is comprised of LED 11 andphoto-transistor 12. The adjustment for the type of documents beinghandled is provided for by adjustable resistor R3 having adjustable armR3a. One terminal of resistor R3 is connected to voltage source +VDC.The opposite terminal of resistor R3 is coupled through fixed resistorR4 to the anode of LED 11, whose cathode is coupled to the collector oftransistor Q1.

The photo-transistor 12 has its emitter coupled to ground and has itscollector coupled in common to the base of transistor Q2 and oneterminal of adjustable resistor R5, whose other terminal is connected incommon to the source +VDC and to the collector of Q2 through resistorR6. The emitter of Q2 is coupled to ground through R7 and to the base oftransistor Q1 whose emitter is coupled to ground and whose collector iscoupled to the anode of LED 11.

The operation of this circuit is as follows:

When energized, the maximum intensity of the light L emitted from LED 11is controlled by the adjustment of resistor arm R3a. With this basicadjustment, light of a predetermined intensity is directed towardphoto-transistor 12. The amount of light reaching photo-transistor 12 isdependent upon the light transmission characteristics of the document(or documents) passing therebetween. Presuming the light transmissioncharacteristic is high, the photo-transistor will approach saturationcausing maximum or near maximum current to be present in the collectorcircuit, developing a large IR drop across R5, dropping the voltage atthe base of Q2. This results in a drop in the emitter current, causing asmall IR drop to be developed across R7 thereby dropping the voltageapplied to the base of Q1. The above circuit coupled to LED 11automatically regulates (and in this case drops) the current flowtherethrough so as to regulate the intensity of its light output.Obviously for low light intensity, the reverse operation occurs whereinwhen a low magnitude current flows through photo-transistor 12 a smallIR drop develops across R5 developing a larger voltage applied to thebase of Q2 and hence a larger IR drop across R7, increasing the voltageapplied to the base of Q1 and thereby increasing the current through theLED 11 and hence the brightness of the light output.

This unique circuit utilized the feedback technique described here andabove for the purpose of maintaining the output of the photo-transistorsubstantially constant and significantly reducing the output of LED 11so as to greatly increase its useful operating life.

The output developed by the collector of Q1 is in fact utilized as thesignal which may be said to be equivalent to those signals representedby the waveforms W2 and W3 of FIG. 1d.

This signal level is applied to the inverted input of a first comparator14 and to the non-inverted input of a second comparator 15. Thenon-inverted input of comparator 14 is coupled to a voltage source +VDCthrough resistor R8 which together with fixed resistors R9 and R10 forma voltage divider circuit which serve as the threshold voltage levels,as will be more fully described.

A capacitor C1 couples the inverted input of comparator 14 and thenon-inverted input of comparator 15 to a reference potential as shown.

The output of comparator 15 is coupled between the terminals ofresistors R11 and R12 shown. Resistor R11 is coupled to the voltagesource +VDC while the resistor R12 is coupled to reference potentialthrough capacitor C2. A diode D1 is coupled in parallel across resistorR12.

The common terminal between R12 and C2 is coupled to one input of NORgate 16 which is coupled to the reset input R of bi-stable flip-flop 17.

The output of comparator 14 is coupled to voltage source +VDC throughresistor R13 and the output is further coupled in common to the reset Rinput of a bi-stable flip-flop 18.

The operation of the first comparator circuit comprised of comparator 15is as follows:

Light emitted from LED 11 is directed toward photo-transistor 12. Theintensity of the light reaching photo-transistor 12 is a function of thelight transmission characteristic of the bill or other document passingtherebetween. The automatic adjustment of light output intensity for LED11 is controlled by the feedback circuit comprised of transistors Q1 andQ2 and their associated resistors R5 and R7, as was described here andabove.

The output signal from the sensing circuit is taken from the collectorof Q1 and is applied to the non-inverting input of comparator 15. Athreshold level is established at the inverting input of comparator 15by means of the voltage divider resistors R8 through R10, connected inseries between +VDC and ground reference. The signal transitions aboutthe threshold level cause the comparator to generate the square pulsesignals shown in FIG. 1e which result from the passage of single billsand double fed bills, respectively.

The square pulse output signals are sustained so long as the transitionsare above the threshold level as shown by waveform W4 is for single feddocuments. The current output as shown by waveform W4 is directlycoupled through diode D1 to capacitor C2 which charges at a rateestablished by the resistors R11 and R12 and diode D1 in circuittherewith.

The individual pulses are integrated as shown by the waveform W5.However, it can be seen that these pulses are significantly separated intime and are each individually brief in duration so that the pulses donot combine with one another to exceed the threshold level Th3.

On the other hand, when double fed documents pass between LED 11 andphoto-transistor 12, the duration of either single transition alone ortaken together with the number of transitions occuring, combine to raisethe output signal at terminal 17 to a level above threshold Th3sufficient to provide a signal indicative of the passage of double feddocuments.

This signal is applied through NOR gate 16 to the reset input R of abi-stable flip-flop 17, whose set input S is coupled to reset meanswhich functions to reset the document handling device after theoccurence of double fed documents in readiness to clear this conditionand begin new counting.

When the threshold level Th3 is reached, the output of Nor gate 16 goesnegative causing the bi-stable flip-flop to be reset whereby the signallevel at its Q output serves to energize an audible alarm and a brakingcircuit which halts the handling of documents following the doubles feddocuments so that the last documents to be fed to an outfeed hopper arethe double fed documents.

As was mentioned above, it is necessary to select the threshold level sothat the apparatus is in actuality set for the detection of doubles feddocuments for the type of documents being run.

For example, the operator may begin to run documents through thedocument handling and counting apparatus without paying direct attentionto the last setting of the doubles detector device which setting may bethe improper setting for the type of documents being run.

Thus the doubles detector circuit includes comparator 14 which servesthe function of preventing the erroneous processing of documents in thefollowing manner:

If the brightness limit of LED 11 is set too high, then single feddocuments will not produce a signal which is applied to the (-) input ofcomparator 14 sufficient to cross the (+) input threshold voltage. Thusno output will be produced to reset flip-flop 18, and will therebyindicate a double. On the other hand, if the brightness limit of the LED11 is set too low, even though comparator 14 will reset flip-flop 18,comparator 15 will provide a tripping signal to gate 16 even whenhandling single fed documents.

The output of comparator 14 is coupled to the reset input R of bi-stableflip-flop 18 whose set input S receives an input indicative of thepresence of the leading edge of the document.

This sets the bi-stable flip-flop 18 so that its Q output is high. Whensingle document detection occurs, a signal applied to reset input R ofbi-stable flip-flop 18 causes the output Q to go low. This signal levelis applied to one input of NAND gate 20, whose other input receives asignal indicative of the fact that the trailing edge of the document hasoccurred. In the event that a single detection has not occurred, the Qoutput of bi-stable flip-flop 18 will remain high, which conditiondevelops a low level at the output of NAND gate 20 at the trailing edgeof the document which, when coupled through NAND 16, applies a resetsignal to the reset input R at bi-stable flip-flop 19 to provide a levelof the Q output of this flip-flop indicative of the fact that double feddocuments have passed between LED 11 and photo-transistor 12. Thus anautomatic means is provided for indicating a doubles fed documentcondition even when such condition does not really exist, in order tohalt the apparatus and alert the operator to move the control knob tothe proper setting for the type of documents being handled. Since this"artificial" condition will occur for single fed documents, thecondition will occur each time a single fed document passes through LED11 and photo-transistor 12 to absolutely assure that the operator willdirect attention to the setting of the doubles sense circuit.

Since conditions sometime arise wherein documents are not fed so thatone is exactly on top of the other but overlap each other onlypartially, it is important to detect this condition since theoverlapping clearly prevents these two documents from being detected andcounted as two documents, the result being that the documents will bedetected as one unusually "long" document. In order to be apprised ofthis condition, the circuitry of FIG. 3 may be employed. FIG. 3a showsthe manner in which two such documents S1 and S2 may overlap. FIG. 3bshowing the end view thereof. The manner of such detection is to selecta time out period of a duration greater than the time required for thesingle fed non-overlapping documents to pass between the counting sensecircuit. The counting sense circuit is comprised of basically the sameelements, i.e. an LED 11 and a photo-transistor 12 arranged on oppositesides of the path of movement of the documents through the documenthandling and counting apparatus. A count pulse is generated asrepresented by the waveform W8 of FIG. 3, which pulse is at the "1"level over the length of the document or over a time interval t2-t1which is equal to the time required for the document to pass between theLED photo-transistor combination. The positive level pulse is integratedthrough resistor R30 and capacitor C5, whose common terminal is coupledto the non-inverting input of a comparator 25. The inverting input iscoupled to a common terminal between resistors R31 and R32 coupledbetween the +VDC voltage source and ground for establishing the properthreshold level at the non-inverting input. If the count pulse has apulse interval greater than that for single fed documents, the thresholdlevel will be surpassed causing the development of a timeout signal atthe output of comparator 25. For example, let it be assumed that thedocuments being handled have a length of 2.5 inches measured in the feeddirection. Thus the maximum length of two such documents which overlapvery very slightly is approximately 5.0 inches. By selecting a thresholdlevel less than the time required for a 5 inch document to pass betweenthe photo-transistor and LED and significantly greater than the timerequired for a single fed document to pass therebetween, an adequatetimeout signal will be provided to sense this condition and abruptlyhalt the equipment. In one preferred example, the timeout may be a timeinterval which is equivalent to the travel of a document of about 4.5inches length so that an overlappage of the order of 0.60 inches willprovide an indication of this condition. This capability, coupled withthe capability of detecting the presence of documents which are fed inoverlapping fashion and which overlap over a significantly greaterportion of their surface area, could yield a doubles sense output signalwhile documents which may be overlapping slightly so that theiroverlapping portion may be their highest light transmissivecharacteristic, or are filtered out, will be detected by the timeoutcircuit shown for example in FIG. 3.

The circuitry of FIG. 3, as well as the apparatus for counting documentsmay, as an alternative to the use of integrating circuits, utilizemulti-stage counters. For example, as shown in FIG. 4 the countingcircuit 30 is comprised of an LED 31 and a photo-transistor 32equivalent to that described here and above but now being utilized forthe purpose of counting the documents. The current output ofphoto-transistor 32 is a function of the light impinging thereon, withthe two major light levels being a reduced light level when a documentis positioned between LED 31 and photo-transistor 32 and a highermagnitude light level when a gap is aligned with elements 31 and 32.

The output signal level appearing at the emitter of 32 is passed througha conditioning circuit which may preferably be of the type described inreissue U.S. Pat. No. Re. 29,470 issued Nov. 8, 1977 and assigned to theassignee of the present invention. The purpose of this circuit is toestablish a satisfactory threshold level for differentiating between thepresence of a gap and the presence of a document so as to be able tocompare the output level of the photo-transistor with the thresholdlevel through suitable comparator means as shown for example in FIG. 3aof the aforementioned reissued patent and thereby generate a signalwhich, when at a first discrete level, is indicative of the passage ofthe document and when at a second discrete level is indicative of thepassage of a gap between elements 31 and 32. The output of theconditioning circuit 33 is coupled directly to the reset input R ofmulti-stage counter 34 and is further coupled to the reset input ofmulti-stage counter 35 through inverter 36 and NOR gate 37. Counters 34and 35 may be characterized as "OFF" and "ON" counters respectively,indicative of the fact that they respectively count pulses when a gapand a document are passing between the elements 31 and 32. In thepresence of a gap, the level at the reset input R allows counter 34 toaccumulate pulses from a master clock 38 capable of generating constantfrequency pulses at a frequency for example, of the order of 500 pulsesper second. These pulses will continue to be accumulated whereby apredetermined number of pulses are indicative of the presence of a gapof suitable length. This condition may be detected through theutilization of a decoder gate 39 coupled to one or a plurality ofselected output stages of the counter so that when that count isreached, the counter will provide the desired output. In the examplegiven, it is assumed that when six such pulses from master clock 38 areaccumulated, a gap of adequate length has been detected. Thus the outputof gate 39 goes low causing the triggering of bi-stable flip-flop 40which temporarily stores a count pulse. Its Q output is coupled throughNOR gate 37 to provide the proper level at the reset input of "ON"counter 35 as will be more fully described.

As soon as the gap has been terminated and the document begins passingbetween elements 31 and 32, the level applied to the reset input R of"OFF" counter 34 maintains counter continuously in the reset conditionpreventing pulses from master clock 38 from being accumulated therein.However, this level is inverted by inverter means 36 and applied throughgate 37 to the reset input of counter 35 which is now permitted toaccumulate pulses from master clock 38 for the interval during which adocument is passing between the elements 31 and 32. As was mentionedhere and above, through the accumulation of an appropriate number ofpulses indicative of the fact that an unusually "long" document ispassing between elements 31 and 32, this condition is detected bydecoder gate 41 to generate the timeout signal referred to here andabove in conjunction with FIG. 3. One output of the "ON" counter mayalso be utilized to reset bi-stable flip-flop 40 in preparation for thenext count to be developed therefrom. The Q output of flip-flop 40 isutilized to couple a count pulse to an accumulator (not shown) forproviding a count of the total number of documents processed by thedocument counting and handling device. As an alternative arrangement tothe pulsing of the counters 34 and 35 by master clock 38, these countersmay be pulsed through the use of the magnetic sensor assembly 50 asshown in FIG. 5. The magnetic sensor comprises a coil 51 wound about amagnetic pole piece 52 having at least a portion or one end thereofpositioned immediately adjacent to the teeth 53a of a magnetic timinggear 53 which is mounted upon the shaft of one of the rollers utilizedto drive the documents being handled through the document handling andcounting device. For example, the magnetic timing gear may be securelymounted to the shaft 24 of the acceleration roller identified bydesignating number 38 in FIG. 2a of the above mentioned U.S. Pat. No.4,054,092. In one preferred embodiment, the timing gear may have 64 gearteeth and a two inch diameter so that each count in the counter willrepresent a travel distance of the order of 0.08 inches. As the gearteeth pass the gear sensor winding 51, a current is developed therein asrepresented by the waveform W7.

The signal represented by waveform W7 is applied to the non-invertinginput of comparator 54, whose inverting input is coupled to the commonterminal between resistors R21 and R22, connected in series between thevoltage VDC and ground reference, thus establishing the threshold levelrepresented by the dotted line Th5 shown in FIG. 5. The resulting pulsesare simultaneously applied to the clock inputs C of counters 34 and 35in place of the pulses developed by master clock 38 shown in FIG. 4. Theadvantages of this circuit reside in the fact that since the documenthandling and counting device of the above mentioned U.S. Pat. No.4,054,092 positively drive the documents with effectively no slippage,instead of measuring time and converting time into distance with the useof master clock 38, the magnetic sensing circuit directly measuresdistance thereby directly measuring the size or length of the documentwith greater accuracy.

Thus, regardless of whether an overlap, gap, timeout or doubles feedcondition occurs, the frequency of the pulses will be a direct functionof the operating speed of the device and no reduction in quality oraccuracy will occur due to any changes in the operating speed of thedocument handling and counting device either because of changes in speeddue to deliberate speed change adjustments provided for by manual meansor due to vagaries or spurious conditions within the system therebyproviding a generating means whose pulses are a function of theoperating speed i.e. rotating speed of the shaft upon which the magnetictiming gear is mounted to provide a more accurate sensing means that themaster clock 38.

In applications where it is desired to select between the two generatingsources, the switching circuitry of FIG. 6 may be employed wherein clockpulses from the master oscillator 38 are applied to one input of NANDgate 56 while pulses from the magnetic sensor 50 are applied to NANDgate 57. An input terminal 58 is coupled directly to the remaining inputof NAND gate 57 and is coupled to the remaining input of NAND gate 56through inverter 59. The outputs of NAND gates 56 and 57 are coupled torespective inputs of the NOR gate 60 and by appropriate positioning ofthe run switch 61 it is possible to select either master clock 38 or themagnetic pulse generator 50 to operate the apparatus for respectiveapplications wherein constant speed operation is to be regularlyemployed allowing for the selection of the master clock whereas whenoperation with speed changes will be required or desired the output ofthe magnetic pulse generator 50 may be selected. Although there has beendescribed herein the use of a light sensor or alternatively the use of amagnetic sensor for counting purposes, any other suitable sensing meansmay be employed.

The gates 39 and 41 may be omitted and the accumulated count may betaken directly from one of the outputs of the counter stages (i.e. "1","2", "4", "8", etc.). Also an accumulated counter from either the "ON"or the "OFF" counters 35 and 34 may be employed to generate the pulserepresenting the count of a document.

As a further alternative, a predetermined count accumulated in the "OFF"counter may be employed to prevent the "ON" counter from being reset.For example when a document passes between elements 31 and 32, countpulses from the clock 38 are accumulated in counter 35. If a punchedhole or the like passes between the elements 31 and 32 it will cause thelight intensity reaching photo-transistor 32 to increase to appear as a"gap". However when the length of the punched hole is much less than thelength of a gap, it is preferred even though the counter 35 stopsaccumulating pulses, that the count accumulated to that point remain incounter 35, to permit the count to be resumed in cases where punchedholes or other perforations are detected.

FIG. 7 shows the circuitry for accomplishing this objective likeelements as between FIGS. 4 and 7 being designated by like numerals.

When no "gap" or "hole" is detected, the low level of document sensephoto-transistor is coupled through inverter 71 and NOR gate 72 andinverter 73 to apply a high level to the reset input "R" of OFF counter34 preventing the OFF counter from accumulating counts. The low level isalso coupled to one input of NAND gate 74 which maintains the output ofNAND gate 74 high. This high output drives the output of nor gate 75 lowto enable on counter 35 to accumulate count pulses from master clock 38.

When four counts are accumulated Q3 output of counter 35 applies a pulseof reset input R of flip-flop 77 driving its Q output low driving theoutput of NAND gate 74 to maintain its output high and thereby maintainthe output of NOR gate low to allow counts to cintinue to beaccumulated, the accumulation of four counts being assumed to identify avalid document.

When a "hole" is detected the input to inverter 71 goes high causing theoutputs of inverter 71, gate 72 and inverter 73 to go low, high and low,respectively, enabling OFF counter 34 to accumulate a count while ONcounter continues to accumulate counts at the pulse rate. When eightpulses are accumulated, the Q4 output, coupled to the set input S offlip-flop 78, sets the flip-flop to apply a level to NAND gate 80causing inverter 81 to apply a level to one input of gate 82 and the setinput S of flip-flop 83.

Gate 82 is coupled through NOR gate 16 (see FIG. 2) to reset the DOUBLESflip-flop 19 (see FIG. 2).

When the count in ON counter 35 reaches 20 the Q3 and Q5 outputs gohigh, driving the output of NAND gate 88 low applying a high to oneinput of NAND gate 90 through inverter 89. The middle input of gate 90is high when flip-flop 83 is reset. The remaining input is high whenhandling normal documents causing the output of gate 90 to go low,driving the output of NOR gate 91 high to set the Q output of TIMEflip-flop 92 high which is employed to turn off the document handlingdevice motor and activate an alarm.

When the count in ON counter 35 reaches 32 and either the normal sizedocuments setting is chosen by moving switch means SW1 to the properposition, or the first document is not being counted, NOR gate 93 goeshigh driving the output of NAND gate 94 low enabling gate 91 to set theTIME flip-flop 92 to activate the alarm and turn off the motor as wasdescribed above.

The FIRST document flip-flop is employed to provide an additional delaywhen the document handling device is restarted after clearing a jam orcompleting a batch of documents whereupon the device has stopped,leaving the leading edge of the next document to be passed between thecount sensor 12 (see FIG. 2) a distance typically in the range from0.125 inches to 0.75 inches from the sensor 12.

The device must accelerate this document from a rest condition to normaloperating speed which requires more time for this document to pass thesensor 12 than succeeding documents. This problem is not encounteredwhen using a magnetic pulse generator of the type shown in FIG. 5.

The "1st" document flip-flop has its Q output set low when a batch iscompleted, when the manual reset is depressed or when an idle stopsignal is generated. Any one of these conditions are passed by NOR gate97 to the reset input R of flip-flop 83 to set its Q output low andprevent gate 94 from generating an output indicative of a "long"document.

The Q output is also coupled through inverter 95 to drive one input ofgate 76 high so that the first count of OFF counter drives its outputlow causing gate 75 to place a high level on the reset input R of ONcounter 35 to prevent the counter from accumulating any counts. When twocounts are accumulated by OFF counter 34, its Q2 output applies a signalto set input S of "1st" flip-flop 83 through gate 80 and inverter 81 todrive the Q output high. Inverter 95 thus places a low level to oneinput of gate 76 maintaining it high to cause gate 75 to remove thereset level from reset input R of ON counter 35 enabling count pulses tobe accumulated. This operation provides a delay of a time sufficient toallow the first document to accelerate to normal counting speed withoutaccumulating a number of counts representative of a long document.

An accumulated count of two in OFF counter 34 is used to reset flip-flop78 and set flip-flop 77.

The OFF counter is preferably provided with a sufficient number ofstages to provide a count at output Qx to generate a signal indicating agap of about 250 millisecond length to sound an alarm identifying anunusually long gap between documents and an output Qy which sets aflip-flop 99 whose Q output goes high to stop the handling and countingdevice when a "gap" of 15 seconds duration is detected, indicating thatno documents have been counted for that period.

The circuitry shown in FIG. 7 also has the capability of providing forhighly simplified calibration of the doubles detection level.

For example, when changing from one type of document to another, it isimportant to set the doubles detector adjustable resistor element to besure that the light element 11 (see FIG. 2) emits light of the properintensity to prevent a single fed document from erroneously creating adoubles detection signal and likewise to prevent a doubles fed conditionfrom failing to generate a doubles detection signal.

This is accomplished by moving switch arm 13a to its OFF position.Documents are run with the knob (R3A) set to enable light element 11 toprovide its brightness output.

The stationary (OFF) contact 13b couples resistor R30 to groundreference placing a low level at one input of NAND gate 111 (FIG. 7).This keeps the output of NAND gate 111 high regardless of the level atits remaining input. A motor braking circuit 113 is responsive to a lowlevel at its input 113a to stop the feeding of documents. Thus the OFFposition of the doubles detection switch prevents the doubles conditionfrom affecting the motor control circuit even if a doubles condition issensed.

An observable DOUBLES condition capability is provided by the currentdriver circuit 110 and "DOUBLES" lamp 112. Whenever a doubles conditionis sensed (as described in connection with FIG. 2) the Q output of thedoubles detection circuitry goes high to apply a high level to currentamplifier 110 and gate 111. The high level applied to the currentamplifier causes lamp 112 to light providing a visual indication of adouble feed condition, regardless of the fact that the double detectionswitch 13' is ON or OFF--when ON the gate 111 will be enabled to createa low condition at its output when both of its inputs are high toactivate the motor control circuit 113 and turn the motor of thedocument handling device off and preferably activate braking means (notshown) in addition thereto. These capabilities form part of theapparatus described in the above mentioned U.S. Patents. For example,see motor M and brake 131 in FIG. 2 of U.S. Pat. No. 3,857,559.

The circuitry of FIG. 8 may also be used to great advantage assemi-automatic means for adjusting the brightness level when the type ofdocuments being processed are changed.

To accomplish the adjustment the doubles detection switch is moved tothe OFF state to prevent any turn-off of the unit in the event of anydouble feeds.

The control knob K mechanically coupled to adjustable resistor switcharm R3A (see FIG. 2) is rotated counter-clockwise to the LIGHT positionto set element 11 for its highest light output (i.e. for the darkest orleast light transmissive documents). If the light output is too high,flip-flop 18 is prevented from being reset by comparator 14 to indicatethe presence of a double.

Turning the knob K to the dark setting (i.e. for very thin or highlylight transmissive documents) comparator 15 will cause even a singledocument to provide a double feed signal. Adjustment is made by turningknob K clockwise so that its indicator I is aligned with the nextgraduation to the right of "DARK" setting and running the documentsthrough again. If the lamp lights again, repeat the operation (i.e.moving one graduation to the right) until the lamp 112 remains offthereby yielding a simple and yet rapid method for setting the properthreshold level.

Whenever lamp 112 is lit, it may be turned off by depressingnormally-open reset button Br to reset the DOUBLE flip-flop 19 (FIGS. 2and 8).

The arrangement of FIG. 8 provides the equipment with the additionalcapability of being able to run documents at high speed and be advisedof the occurrence of a doubles condition (or conditions) each time lamp112 lights, without stopping the equipment each time. Stacks ofdocuments yielding a doubles indication may be set aside for evaluationat a later time, enabling counting and processing to continue at highspeed with no stopping but with a doubles sensing capabilitycontinuously monitoring the processing operation.

I claim:
 1. Sensing means for distinguishing between single and doublefed documents moving along a feed path at spaced intervals so that thetrailing edge of each document is normally spaced from the leading edgeof the next succeeding document, said means comprising:sensing meansincluding a light sensing element positioned to one side of said path; alight source positioned on the opposite side of said path and aligned sothat its light rays are directed toward said light sensing element;comparator means for comparing the output of said light sensing means,which varies as a function of the light transmission characteristic ofthe passing documents, against a predetermined threshold for generatinga constant level output when the level of the sensing means outputreaches the threshold valve; means coupled to the output of saidcomparator means for averaging the signal at said comparator meansoutput; and means for generating a doubles sense signal when the levelof the averaged signal reaches a predetermined threshold.
 2. The sensingmeans of claim 1 wherein said light source is a light emitting diode. 3.The sensing means of claim 1 wherein said light sensing element is aphoto-transistor.
 4. The sensing means of claim 3 wherein the currentoutput of the photo-transistor is increased as the light intensityincreases until the photo-transistor reaches saturation, at which timethe current output remains constant regardless of increasing lightintensity; andadjustable brightness control means for controlling theoutput of the light source to lie within a brightness range whose upperlimit is chosen to prevent the photo-transistor from going intosaturation for the type of documents being sensed so that thedifferences in output levels as between single and double fed documentsare maximized.
 5. The sensing means of claim 4 wherein the adjustablebrightness control means comprises a power supply source and adjustableresistance means for adjustably limiting the current supplied to saidlight source by said power supply source.
 6. Apparatus fordistinguishing between single and double fed documents moving along afeed path at spaced intervals so that the trailing edge of each documentis spaced from the leading edge of the next succeeding document, saidmeans comprising:sensing means including a light sensing elementpositioned to one side of said path; a light source positioned on theopposite side of said path and aligned so that its light rays aredirected toward said light sensing element; comparator means forcomparing the output of said light sensing means, which varies as afunction of the light transmission characteristic of the passingdocuments, against a predetermined threshold for generating a constantlevel output when the level of the sensing means output reaches thethreshold value; means responsive to the output of said light sensingelement for controlling the brightness of the light output of said lightsource so that it is inversely proportional to the magnitude of theoutput signal generated by said light sensing element.
 7. The apparatusof claim 6 further comprising current limiting transistor means having acollector coupled in series with said light source and having a basecontrolled by the output of said controlling means to limit the currentsupplied to the light source.
 8. The apparatus of claim 7 wherein saidcontrolling means includes current amplification means for supplyingample operating current to the base of said current limiting transistor.